I now have done some impulse measurements with a microphone. All the measurements shown here have been done with the microphone at the listening position.

The picture numbered 1 corresponds to the LS standing in a "conventional" way. The distance between the LS and the mic is 2,3m (7,5 feet). The impulse is not that great but still quite near what is “commonly” accepted for loudspeakers. The large peak at 0,8 ms correspond to a reflexion inside the box where the damping material is placed. Needle felt is placed in the middle of the depth of the speakers, which are 30 cm deep (12 inches). I will try other damping materials and maybe other positioning of it in the future.

The picture numbered 4 corresponds to the LS lying along the side walls (as shown here). The distance between the mic and the LS is 2,5 meter (8,2 feet) in this case. I had to enter this distance manually since the measurement program considered the large peak at around 5 ms as the direct sound! This peak corresponds to the roof reflexion, meaning that I was listening mostly to the roof… This might explain my impressions of spaciousness and 3D feelings.

After a while, the euphoria due to the different sound went down and I moved my speaker back to the conventional way where I have a much better tonal balance.

Originally posted by Etienne88
I now have done some impulse measurements with a microphone. All the measurements shown here have been done with the microphone at the listening position.

great!
the measurements clearly confirm that the loudspeaker cannot be heard in such a positioning as a distinct source of sound
which is a good thing – a key to realistic sound
and this is all the measurement really shows

Quote:

Originally posted by Etienne88
This peak corresponds to the roof reflexion, meaning that I was listening mostly to the roof… This might explain my impressions of spaciousness and 3D feelings.

Well, strictly speaking You were certainly not "listening to the ceiling"!
You were listening to the music instead of listening to the speakers
tell me - had you an impression that "sound comes out of the ceiling"?

reflection off the ceiling and all other reflections in such a positioning are not perceived as distinct sound sources, just like the speakers
it is just a sequence of reflections that occur in the room and that carry the left-right signal encoded in a stereo recording

Quote:

Originally posted by Etienne88
After a while, the euphoria due to the different sound went down and I moved my speaker back to the conventional way where I have a much better tonal balance.

much better that is…?
can You give more details?
tonality can be or in case of a fullranger positioned in such a way even should be corrected by means of equalization, passive or active
and what about other things You wrote about?

Quote:

Originally posted by Etienne88
2) the bass output is much stronger. ( …) I can now locate where the bass is coming from what I couldn't do before. It is not pin point localisation but still!
3) I am not sure if the room disappeared but I can say that there is a feeling of space that I did not have before. For example, with a recording made in a church, the church has become much bigger than before.
4) I will tend to say that I have a more 3D feeling but I lost some depth, that for sure! the 3D feeling might come from the LS positioning but as well from the fact that I don't see the drivers any more (they are hidden from my view by two couches that are facing each other along the side walls).
5) this one seems a bit contradictory to me and it is kind of hard to explain: I have deeper silences between the notes but it doesn't sound as clear as with the drivers facing me. The "deeper silences" thing comes from the fact that I can now hear some noises from the CD player while listening to music! About the clear sound: I have the feeling that I am much far away from the musicians than before. This is maybe linked to the lake of treble I feel with this set up...
6) The sweet spot has grown for a tiny little spot to an area!

what about the bass? feeling of space? 3D? deeper silences between the notes? "sweet area"?

by returning to standard positioning without first trying frequency equalisation didn't You "throw out the baby with the bath water"?

Originally posted by graaf
tell me - had you an impression that "sound comes out of the ceiling"?

Not directly, it comes from higher than with the speakers in a conventional way... Unfortunately we are not very good at locating thing in the vertical plan!

Quote:

Originally posted by graaf
much better that is…?
can You give more details?

I will try!
If you look at the attached chart, it shows the psychoacoustic response calculated from the impulse response I posted earlier. (I don't know about the real value of the psychoacoustic response but you might find more info here). curves 1 and 2 are from the LS positioned in a conventional way. Curves 3 and 4 are from the LS lying along the side walls with the correct delay. Curves 5 and 6 are from the LS lying along the side walls with the automatic delay.
You can see that with the LS lying the response drops regularly from 500 Hz upwards which I cannot correct with the tone controls of my current amplifier. At the end, the correction would have "linearized" the frequency response but it would have done nothing to the time domain.

Quote:

Originally posted by graaf
and what about other things You wrote about?
what about the bass? feeling of space? 3D? deeper silences between the notes? "sweet area"?

I already explained the bass, the bass output is increased by the fact that the speakers are closer to the floor and side walls. Between a little deeper bass + missing highs and less deep bass with acceptable highs, I chose the second one!
The feeling of space and 3D might come from the roof reflexion...
The deeper silences between the notes most probably come from the excitement or euphoria!
The sweet spot is now smaller but I have more depth.

As you can see, it is not all black or all white! Both positioning methods have advantages and drawbacks. The "conventional" positioning is to my opinion the best compromise for my loudspeaker-room combination.

Originally posted by Etienne88
You can see that with the LS lying the response drops regularly from 500 Hz upwards

well, OBJECTIVELY it is much better balanced than in case of conventional positioning
the black and green curves (1 and 2) are clearly the worst - thin and bright sound
the orange curve (6) although whith attenuated highs is still clearly the best balanced of all

Quote:

Originally posted by Etienne88
which I cannot correct with the tone controls of my current amplifier.

not with tone controls but even simple passive equalization of the BSC (baffle step correction) type could do the job

Quote:

Originally posted by Etienne88
At the end, the correction would have "linearized" the frequency response but it would have done nothing to the time domain.

and what is wrong with time domain? Did You hear anything wrong which could be attributed to the time domain distortions? What was it?
I think that You are really suggested by the impulse response measurement which You misinterpret

Quote:

Originally posted by Etienne88
Between a little deeper bass + missing highs and less deep bass with acceptable highs, I chose the second one!

with simple equalization You would have those desired highs

BTW Your "psychoacoustic response" of the conventional setup (curves 1-2) shows bright, excessive highs and higher midrange (typical for such a Fostex and usually corrected with apropriate RLC) plus lower midrange suck out
both things typical for typical audiophile sound and for me quite unacceptable, highly unrealistic, unnatural
but, well, this is all of course very subjective

Quote:

Originally posted by Etienne88
The feeling of space and 3D might come from the roof reflexion...

well, "might"...
this doesn't mean that it is an artificial "ceiling effect"
the decisive test is whether different recordings sound more similar one to another with conventional positioning or with the unconventional
the question is whether the "3D" You experience is uniform and the same for different recordings (="it’s an added ceiling effect") or is it different for different recordings (="the system reveals 3D that is in the recording and that is lost in conventional stereo setup")

Quote:

Originally posted by Etienne88
The deeper silences between the notes most probably come from the excitement or euphoria!

I tried to find out the tilt angles (inwards/upwards) of the Carlsson orthoacoustic speakers (50/51/52 series). I don´t speak swedish and registering at carlssonplanet failed. It would be very kind if you could help me.

I choose to have a wide band speaker for simplicity reasons. I wanted first to avoid filter since I have almost no idea how they work, but I would like to learn! So unless you teach me or you serve me the appropriate filter on a silver plate I will live with my speakers as they are!

Quote:

and what is wrong with time domain? Did You hear anything wrong which could be attributed to the time domain distortions? What was it? I think that You are really suggested by the impulse response measurement which You misinterpret

I did not hear anything wrong, no. But I trust better my microphone than my brain!
How do you interpret the impulse response from the lying speakers?